You can( and have to) be what kind police officer(Drug department, S.W.A.T. etc...) you want in the R.T.P.D.
Look example from my profile.

Name: Tepe Richardson
Age: 29
occupation: R.T.P.D. police officer
Number: 63-93
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Tepe stops his police car behind a red Honda. "This is 63-93. I request backup to code-3 situation. Red Honda, maching the description to murder on Hensson street. Over" Tepe said into his radio. "*static* 63-93, this is 51-42, I will be there in two minutes *Static*" Tepe heard from the radio. He waited for two minutes and a police car drove behind his. Tepe opened the door. "63-93, covering from the passenger side" Tepe heard the man saying as he walked to the police car's side. Tepe rose from the car and drew his gun and ointed it towards the car. "This is RTPD! Come out from the car with your hand's up!" Tepe shouted and heard the door open. A man came out from the car with his hands up. Tepe walked few steps towards the man. "Get on the ground!" Tepe shouted and the man went to the ground. Tepe holstered his weapon and cuffed the man. "Get up" Tepe commanded and the man rose. Tepe checked the man and found only an wallet and a knife. Tepe then checked the car as the other police officer watched the man. Tepe found a Magnum 45. from the back seat and turned to the man. "You have the right to remain silent. What you say me be used against you in a court of law. You have the right to an attourney. If you you cannot afford a attorney, one will be appointed to represent you before questioning if you wish" Tepe said and pushed the man towards his police car. The other police radioed something as the man sat down on th police car. Tepe closed the backdoor and went sitting on the drivers seat. Tepe drived towards the jail.

"Our posturings, our imagined self-importance,
the delusion that we have some privileged position in the universe,
are challenged by this point of pale light.
Our planet is a lonely speck in the great enveloping cosmic dark.
In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves."
- Carl Sagan

Vader's wife was very pregnant when she died 19 years ago. All of a sudden a 19 year old who is very strong in the force and has a distinct resembalance to him in his younger days rolls in from Vader's home planet with his old Master Obi-Wan (Who was the ONLY other person preset at the time his wife died. And to boot, the kid's last name is Skywalker.

So in answer to your question, he knew Luke was his son because his name is Darth Vader, and not Darth Retard.

"Our posturings, our imagined self-importance,
the delusion that we have some privileged position in the universe,
are challenged by this point of pale light.
Our planet is a lonely speck in the great enveloping cosmic dark.
In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves."
- Carl Sagan

Vader's wife was very pregnant when she died 19 years ago. All of a sudden a 19 year old who is very strong in the force and has a distinct resembalance to him in his younger days rolls in from Vader's home planet with his old Master Obi-Wan (Who was the ONLY other person preset at the time his wife died. And to boot, the kid's last name is Skywalker.

So in answer to your question, he knew Luke was his son because his name is Darth Vader, and not Darth Retard.

"Hwo is this?" Tepe asked with an dimanding voice. "What do you want?" He asked. He stopped on the jail and got out of the car. He opened the backdoor and walked the prisoner to the jail.

"Our posturings, our imagined self-importance,
the delusion that we have some privileged position in the universe,
are challenged by this point of pale light.
Our planet is a lonely speck in the great enveloping cosmic dark.
In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves."
- Carl Sagan

"I can't say over the phone. Listen carefully, can you get to Antoine and Sheperd? Please come alone, you may come armed if you wish."

Vader's wife was very pregnant when she died 19 years ago. All of a sudden a 19 year old who is very strong in the force and has a distinct resembalance to him in his younger days rolls in from Vader's home planet with his old Master Obi-Wan (Who was the ONLY other person preset at the time his wife died. And to boot, the kid's last name is Skywalker.

So in answer to your question, he knew Luke was his son because his name is Darth Vader, and not Darth Retard.

"Where to?" Tepe asked, walking back into his car. He radioed for Antoine and Sheperd to be close to him. Soon he heard their cars drive next to the jail.

"Our posturings, our imagined self-importance,
the delusion that we have some privileged position in the universe,
are challenged by this point of pale light.
Our planet is a lonely speck in the great enveloping cosmic dark.
In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves."
- Carl Sagan

"You're not coming alone. Call them off or the meeting is off. I am unarmed. If I was a whack job, would I have this number?"

Vader's wife was very pregnant when she died 19 years ago. All of a sudden a 19 year old who is very strong in the force and has a distinct resembalance to him in his younger days rolls in from Vader's home planet with his old Master Obi-Wan (Who was the ONLY other person preset at the time his wife died. And to boot, the kid's last name is Skywalker.

So in answer to your question, he knew Luke was his son because his name is Darth Vader, and not Darth Retard.